When we are considering attic insulation, there are several factors that we should keep in mind. There are two main types of blow in attic insulation. These two are most commonly used. They are cellulose and fiberglass insulation. Also there is the blow in rock wool insulation but the use of it is not so common.
Cellulose, which is most commonly used, is a natural product of wood. It is primarily made out of natural newspaper. To meet the smoke development and flame spread requirements of today’s building codes; a fire retardant chemical is added to the cellulose. The fiberglass insulation material that is used is the same material that batts or roles of the fiberglass insulation except for the fact that it is chopped or cubed so that it can be easily installed with the help of the insulating blowing machine. The fiber glass insulation will typically consist of 20% to 30% of recycled glass.
The r value of the cellulose that is used is R-3.2 to 3.8 per square inch. The loose filled fiberglass will have an R-value of R-2.2 to 2.7 per inch cube. To achieve the desired R value, you will have to depend on both the depth of the insulation as well as the density.
There are varying R values for ceiling insulation based upon the energy codes as well the climate of your locality. Based on the type of attic that you have, the code requirements may also vary. For example for joist assembled roof assemblies as well as for attics with single rafter may vary. There is a typically a chart on the insulation bag that will have the accurate depths for the various R values.
There are depth markers that are required to be placed in attic space which the WSEC requires to help the inspector and the installer verify the depth of the insulation. These depth markers should be placed within every three hundred square feet of the attic area and these must face towards the attic.
The depth of the insulation is very important; however, checking the density of the insulation is also equally important. The blow in insulation type can be fluffed up after it is installed. This is done so that it meets the required depth without actually meeting the required R value. This will settle over time so that the desired R value is achieved as the R value is lowered after it settles down.
The attic card is the easiest way to document the amount of R value installation. These are usually found stapled near the attic access to the truss. This card will also have information that is cited by the federal trade commission. Sometimes a chart is also attached with this.